advance of the supporting
member.

[Illustration: Fig. 24. Testing Work with Dial Indicator]

=Centering Parts to be Turned.=--As previously mentioned, there are a
number of different methods of forming center-holes in the ends of parts
that have to be turned while held between lathe centers. A method of
centering light work, and one that requires few special tools, is first
to locate a central point on the end and then drill and ream the
center-hole by using the lathe itself. Hermaphrodite dividers are useful
for finding the center, as illustrated at _A_, Fig. 25, but if the work
is fairly round, a center-square _B_ is preferable. A line is scribed
across the end and then another line at right angles to the first by
changing the position of the square; the intersection of these two lines
will be the center, which should be marked by striking a pointed punch
_C_ with a hammer. If a cup or bell center-punch _D_ is available, it
will not be necessary to first make center lines, as the conical part
shown locates the punch in a central position. This style of punch
should only be used on work which is fairly round.

[Illustration: Fig. 25. Centering End with Punch preparatory to
Drilling]

After small centers have been located in both ends, their position can
be tested by placing the work between the lathe centers and rotating it
rapidly by drawing the hand quickly across it. By holding a piece of
chalk close to the work as it spins around, a mark will be made on the
"high" side if the centers are not accurate; the centers are then
shifted toward these marks. If the work is close to the finished
diameter, the centers should, of course, be located quite accurately in
order that the entire surface of the work will be turned true when it is
reduced to the finished size.

One method of forming these center-holes is indicated in Fig. 26. A
chuck _C_ is screwed onto the spindle in place of the faceplate, and a
combination center drill and reamer _R_ is gripped by the chuck jaws and
set to run true. The center is then drilled and reamed at one end by
pressing the work against the revolving drill with the tailstock
spindle, which is fed out by turning handle _n_. The piece is then
reversed for drilling the opposite end. The work may be kept from
revolving while the centers are being drilled and reamed, by attaching a
dog to it close to the tailstock end and then adjusting the cross-slide
until the dog rests upon the slide. Ma